This application is a national phase of PCT/FR00/00968, filed Apr. 14, 2000, and International Application No. 99/04801, which was filed on Apr. 16, 1999, and was not published in English.
The invention relates to a shaping tool, intended for use in the manufacture of profiled parts made of a composite material for final polymerisation of these parts. It is particularly applicable to the manufacture of parts with a U or L cross-section.
According to one conventional manufacturing technique, profiled parts made of a composite material, and particularly parts with a U or L cross-section, are usually made by laying up fabrics or layers of fibers impregnated with a thermosetting or thermoplastic resin in order to obtain a part blank with the required shape and dimensions, and then polymerising this part blank in an autoclave.
Normally, the final polymerisation step is done using a shaping tool comprising a rigid metallic mould in the shape of a punch on which the part blank is placed. The tooling also comprises a leak tight bladder that covers the outside of the part blank and inside which a vacuum is created in order to create the shape of the blank by pushing it against the punch shaped mould.
This tooling is placed in an autoclave in order to apply the temperature and pressure cycle necessary for polymerisation of the resin used.
This cycle includes a temperature rise during which the metallic mould expands. When polymerisation of the resin is complete, the tooling and the part contained in it are gradually cooled down to ambient temperature. During cooling, the shrinkage of the hardened part is very much less than the shrinkage of the punch shaped metallic mould. Therefore, the part is easily removed from the mould when the tooling is extracted from the autoclave.
This conventional production technique is satisfactory in some cases. However, it is not suitable when the profiled parts to be made have a calibrated outer surface, in other words when this surface must be perfectly free of geometric faults and when its dimensions must be accurately controlled. This requirement occurs particularly when the functional surfaces of the parts to be made are the outside surfaces of these parts.
In the conventional technique described above, the outside surface of the profiled parts is shaped directly by the flexible leak tight bladder. Therefore, uncontrollable geometric and dimensional defects will necessarily be present.
The purpose of the invention is precisely a shaping tool, intended for the polymerisation of profiled parts made of a composite material, with an innovative design that enables it to make parts in which the outer surface is practically free of geometric and dimensional defects, and which has mechanical characteristics similar to those obtained with existing tools without fundamentally modifying the polymerisation technique.
According to the invention, this result is obtained by means of a shaping tool, for the polymerisation of profiled parts made of a composite material comprising a rigid mould, and shaping means suitable for pushing a part blank into contact with the rigid mould, the tooling being characterized in that the rigid mould is formed of several elements without any connection between them, holding means being provided to keep the said elements normally in contact wit with each other so as to define a cavity inside which the part blank can be fitted, while enabling the said elements to separate during a cooling phase following polymerisation of the blank.
According to the invention, the outer surface of the part is calibrated using a hollow mould, with a cavity in which the part blank is placed.
Furthermore, the shrinkage of the mould that occurs during the cooling phase after polymerisation has no effect on the mechanical properties of the part. Production of the mould in several independent elements means that these elements can be separated from each other during cooling. Therefore, the part is not affected by any excessive stresses due to shrinkage of the mould. Furthermore, keeping the elements forming the mould in contact with each other throughout the polymerisation time guarantees that the required shape and dimensions will be obtained.
In one preferred embodiment of the invention, the support means comprise means of applying pressure on an outside face of at least one of the elements of the mould, in order to push this element towards an adjacent element.
Preferably, although not necessarily, the outside face of this element is approximately parallel to an inside face delimiting the cavity from the said element or a counter form placed inside this element.
In the preferred embodiment of the invention, the elements of the rigid mould are placed in a rigid envelope. The pressure application means then comprise at least one flexible wall connected onto the envelope in a leak tight manner, or a leak tight bladder fixed on the envelope. The flexible wall or the leak tight bladder is laid out so that it is forced under pressure into contact with the outside face of the corresponding element.
When the part to be made has a U-shaped cross-section, the rigid mould forms a cavity that also has a U-shaped cross-section. Furthermore, the mould comprises a central element materializing the bottom of the cavity and two end elements materializing the sides of the cavity. The support means then normally keep the end elements in contact with the side edges of the central element.
In this case, the pressure application means comprise either two flexible walls that can be pressurized to come into contact with the outside faces of each of the end elements, or two leak tight bladders that can be forced into contact with the said outside faces under the effect of pressure output by an external pressure source.
When flexible walls are used, they are subjected to the external pressure.
Furthermore, the cavity may have a variable cross-section or it may be uniform over its entire length.